1. Field of the Invention
This invention relates to a control device for an internal combustion engine and a control method for an internal combustion engine that correct an intake manifold pressure, which is used for calculating control parameter of the internal combustion engine, for humidity.
2. Description of the Related Art
An engine control method called “torque-based control” in which an engine output shaft torque is used as a value of drive power demanded by a driver or a vehicle and the torque generated by the engine is controlled by taking this engine output shaft torque as an indicator has become popular in recent years.
In the torque-based control, the target torque of the engine is determined on the basis of the depression amount of the accelerator pedal by the driver. The throttle opening degree is then controlled such that a target intake air flow rate enabling the generation of the target torque is taken in by the engine. As a result, the engine output is controlled to the target torque by controlling the fuel injection amount or ignition timing according to the actual intake air flow rate, and the travel performance demanded by the driver is realized.
The following technique has been suggested for an engine control device that controls the throttle opening degree by driving an actuator coupled to the engine throttle in order to realize the target intake air flow rate corresponding to such target torque of the engine. Thus, the target opening area of the throttle is determined by using the target intake air flow rate, the ratio of pressure before and after the throttle, and the opening area of the throttle in a basic formula for flow rate calculation in a restriction-type flowmeter. With this technique, the actuator coupled to the throttle is controlled such as to obtain the throttle opening degree at which the target opening area of the throttle is attained.
In order to control, for example, the fuel injection amount and ignition timing, which are the engine control elements, it is necessary to detect the amount of air taken into the engine. Two systems which are called L-Jetronic and D-Jetronic are generally used for such detection.
In the L-Jetronic system, the amount of air which is taken in is detected by an air flow sensor disposed in an intake channel. The D-Jetronic system estimates the amount of air taken into a cylinder on the basis of the intake manifold pressure downstream of the throttle valve and the engine revolution speed.
The D-Jetronic system is inexpensive because no expensive air flow sensor is needed. Another advantage of the D-Jetronic system is that a fast response to changes in the operation state is ensured by control using the pressure immediately before the cylinder.
A method for calculating the amount of air taken into a cylinder from the pressure and volume efficiency of the intake manifold and the cylinder volume and temperature is a specific example of methods for estimating the cylinder intake air amount in the D-Jetronic system (see, for example, Japanese Patent Application Publication (JP-A) No. H08-303293.